This invention relates to the field of borehole telemetry, especially mud pulse telemetry wherein data relating to borehole parameters is gathered by sensing instruments located downhole in the drill string and is transmitted to the surface via pressure pulses created in the drilling mud. More particularly, this invention relates to a pressure balanced hydraulic circuit for operating the mud pulse valve in a mud pulse telemetry system.
The basic concept of mud pulse telemetry for transmitting borehole data from the bottom of a well to the surface has been known for some time. U.S. Pat. Nos. 4,021,774, 4,013,945 and 3,982,431, all of which are owned by the assignee of the present invention, show various aspects of a mud pulse telemetry system which has been under development by the assignee hereof for several years. Those patents also refer to earlier patents which also show mud pulse telemetry systems and various features thereof.
In the course of developing a mud pulse telemetry system, particular attention has been devoted to the hydraulic circuit for actuating the mud valve which creates the pressure pulses to transmit borehole data to the surface. Hydraulic circuits for actuating a mud pulse valve are shown in U.S. Pat. Nos. 3,756,076, 3,737,843 and 3,693,428. While the hydraulic circuits shown in those patents are workable and may be suitable for use in some applications, the hydraulic circuit of the present invention has been developed as the preferred hydraulic circuit configuration for the mud pulse telemetry system of applicant's assignee.